Risk of chronic pancreatitis in carriers of the c.180C>T (p.Gly60=) CTRC variant: case-control studies and meta-analysis

Abstract

Chymotrypsin C (CTRC) is a digestive serine protease produced by the pancreas that regulates intrapancreatic trypsin activity and provides a defensive mechanism against chronic pancreatitis (CP). CTRC exerts its protective effect by promoting degradation of trypsinogen, the precursor to trypsin. Loss-of-function missense and microdeletion variants of CTRC are found in around 4% of CP cases and increase disease risk by approximately 3-7-fold. In addition, a commonly occurring synonymous CTRC variant c.180C>T (p.Gly60=) was reported to increase CP risk in various cohorts but a global analysis of its impact has been lacking. Here, we analyzed the frequency and effect size of variant c.180C>T in Hungarian and pan-European cohorts, and performed meta-analysis of the new and published genetic association data. When allele frequency was considered, meta-analysis revealed an overall frequency of 14.2% in patients and 8.7% in controls (allelic odds ratio (OR) 2.18, 95% confidence interval (CI) 1.72-2.75). When genotypes were examined, c.180TT homozygosity was observed in 3.9% of CP patients and in 1.2% of controls, and c.180CT heterozygosity was present in 22.9% of CP patients and in 15.5% of controls. Relative to the c.180CC genotype, the genotypic OR values were 5.29 (95% CI 2.63-10.64), and 1.94 (95% CI 1.57-2.38), respectively, indicating stronger CP risk in homozygous carriers. Finally, we obtained preliminary evidence that the variant is associated with reduced CTRC mRNA levels in the pancreas. Taken together, the results indicate that CTRC variant c.180C>T is a clinically relevant risk factor, and should be considered when genetic etiology of CP is investigated.

Keywords: Chymotrypsin; Genetic association study; Meta-Analysis; Pancreatitis.

Figure 1.

Flow chart of the study selection process.

Figure 2.

Meta-analysis of the association between the c.180C>T CTRC variant and chronic pancreatitis (CP) in global cohorts. Forest plots are shown. A, Association between the c.180T minor CTRC allele and CP. B, Association of the c.180TT homozygous CTRC genotype with CP. C, Association of the c.180CT heterozygous CTRC genotype with CP.

Figure 3.

Meta-analysis of the association between the c.180C>T CTRC variant and chronic pancreatitis (CP) in European adult cohorts. Forest plots are shown. A, Association between the c.180T minor CTRC allele and CP. B, Association of the c.180TT homozygous CTRC genotype with CP. C, Association of the c.180CT heterozygous CTRC genotype with CP.

Figure 4.

Effect of c.180C>T variant on CTRC mRNA expression. A, Electropherograms showing Sanger sequencing of a cDNA sample from the pancreas of a heterozygous CTRC c.180 C>T carrier. Note the difference in the peak heights at position c.180. B, Relative mRNA expression levels of the c.180T CTRC allele in the pancreas of heterozygous c.180C>T carriers. The gray line and symbols represent the calibration curve; the black triangles denote the pancreatic cDNA samples analyzed (n=10). See Methods for experimental details.